Aggregate particles for use in electrophoretic color displays

Abstract

A multi-color display device has front and rear electrodes on opposed sides of an electrophoretic medium. The device has a voltage controller configured to apply a first and a smaller second potential difference, of either polarity, between the electrodes. The electrophoretic medium has first and second species of particles of differing colors and charge polarities. The first and second particles move independently of one another in response to the first potential difference, but upon application of the second potential difference form charged aggregates, moving as a unit, having an aggregate color different from the first and second colors.

What is claimed is: 
     
       1. A method of driving a multi-color display device, the device including:
 a front electrode and a rear electrode on opposed sides of an electrophoretic medium; 
 a voltage controller configured to apply a first potential difference and a second potential difference, smaller than the first potential difference, of either polarity, between the front and rear electrodes; 
 a rear reflector; 
 the electrophoretic medium having first, second and third species of particles; 
 the first particles having a first color and a first charge polarity and a first charge magnitude, 
 the second particles having a second color, having a second charge polarity different from the first species of particles, and having a second charge magnitude different from the first species of particles; 
 the third particles having a third color, different from the first and second colors, having a third charge polarity different from one of the first and second charge polarities, having a third charge magnitude different from one of the first and second charge magnitudes, wherein the third particle is configured to not aggregate with the first or second particles; 
 the first, second and third particles moving independently of one another in response to the first potential difference applied between the electrodes, but upon application of the second potential difference the first and second particles forming charged aggregates, moving as an aggregate unit, having an aggregate color different from the first, second and third colors; 
 the method comprising: 
 applying the first potential difference of one polarity between the electrodes to move the first, second, and third particles independently of one another, with the first and third particles moving to the rear electrode and the second particles moving to the front electrode to display a second color; 
 applying the first potential difference of the opposite polarity between the electrodes to move the first, second, and third particles independently of one another, with the second particles moving to the rear electrode and the first and third particles moving to the front electrode to display a fourth color; 
 forming aggregate charged particles by applying an alternating electric field, then applying the second potential difference between the electrodes; 
 applying the second potential difference of one polarity to move the aggregate particles to the rear electrode and the third particles to the front electrode to display the third color; 
 applying the second potential difference of the opposite polarity to move the aggregate particles to the front electrode and the third particles to the rear electrode to display the aggregate color. 
 
     
     
       2. The method of  claim 1 , wherein the first color is cyan, the second color is magenta or yellow, the third color is yellow or magenta, and the second and third colors are not the same. 
     
     
       3. The method of  claim 1 , wherein the first color is magenta, the second color is cyan or yellow, the third color is yellow or cyan, and the second and third colors are not the same. 
     
     
       4. The method of  claim 1 , wherein the first color is yellow, the second color is magenta or cyan, the third color is cyan or magenta, and the second and third colors are not the same. 
     
     
       5. The method of  claim 1 , wherein the rear reflector color is white. 
     
     
       6. A multi-color display device comprising:
 a front electrode and a rear electrode on opposed sides of an electrophoretic medium; 
 a voltage controller configured to apply a first potential difference and a second potential difference, smaller than the first potential difference, of either polarity, between the front and rear electrodes; 
 a rear reflector; 
 the electrophoretic medium having first, second and third species of particles; 
 the first particles having a first color and a first charge polarity and a first charge magnitude, 
 the second particles having a second color, having a second charge polarity different from the first species of particles, and having a second charge magnitude different from the first species of particles; 
 the third particles having a third color, different from the first and second colors, having a third charge polarity different from one of the first and second charge polarities, having a third charge magnitude different from one of the first and second charge magnitudes, wherein the third particle is configured to not aggregate with the first or second particles; 
 the first, second, and third particles moving independently of one another in response to the first potential difference applied between the electrodes, but upon application of the second potential difference the first and second particles forming charged aggregates, moving as an aggregate unit, having an aggregate color different from the first, second and third colors. 
 
     
     
       7. A multi-color display device according to  claim 6 , wherein the first color is cyan, the second color is magenta or yellow, the third color is yellow or magenta, and the second and third colors are not the same. 
     
     
       8. A multi-color display device according to  claim 6 , wherein the first color is magenta, the second color is cyan or yellow, the third color is yellow or cyan, and the second and third colors are not the same. 
     
     
       9. A multi-color display device according to  claim 6 , wherein the first color is yellow, the second color is magenta or cyan, the third color is cyan or magenta, and the second and third colors are not the same. 
     
     
       10. A multi-color display device according to  claim 6  having at least five color states. 
     
     
       11. A multi-color display device according to  claim 6  having eight color states. 
     
     
       12. A multi-color display device according to  claim 7 , having eight display color states of blue, yellow, cyan, red, magenta, green, white and black. 
     
     
       13. A multi-color display device according to  claim 8 , having eight display color states of blue, yellow, cyan, red, magenta, green, white and black. 
     
     
       14. A multi-color display device according to  claim 9 , having eight display color states of blue, yellow, cyan, red, magenta, green, white and black. 
     
     
       15. A method of driving a multi-color display device, the device including:
 a front electrode and a rear electrode on opposed sides of an electrophoretic medium; 
 a voltage controller configured to apply a first potential difference and a second potential difference, smaller than the first potential difference, of either polarity, between the front and rear electrodes; 
 a rear reflector; 
 the electrophoretic medium having first, second and third species of particles; 
 the first particles having a first color and a first charge polarity and a first charge magnitude, 
 the second particles having a second color, having a second charge polarity different from the first species of particles, and having a second charge magnitude different from the first species of particles; 
 the third particles having a third color, different from the first and second colors, having a third charge polarity different from one of the first and second charge polarities, having a third charge magnitude different from one of the first and second charge magnitudes, wherein the third particle is configured to not aggregate with the first or second particles; 
 the first, second, and third particles moving independently of one another in response to the first potential difference applied between the electrodes, but upon application of the second potential difference the first and second particles forming charged aggregates, moving as an aggregate unit, having an aggregate color different from the first, second and third colors; 
 the method comprising: 
 applying the first potential difference of one polarity between the electrodes to move the first, second, and third particles independently of one another, with the first and third particles moving to the rear electrode to display a fourth color; 
 applying the first potential difference of the opposite polarity between the electrodes to move the first, second and third particles independently of one another, with the second particles moving to the rear electrode to display the second color; 
 forming aggregate charged particles by applying an alternating electric field, then applying the second potential difference between the electrodes; 
 applying the second potential difference of one polarity to move the third particles to the front electrode and the aggregate particles to the rear electrode to display the aggregate color; and 
 applying the second potential difference of the opposite polarity to move the aggregate particles to the front electrode and the third particles to the rear electrode to display the third color. 
 
     
     
       16. The method of  claim 15 , wherein the first color is cyan, the second color is magenta or yellow, the third color is yellow or magenta, and the second and third colors are not the same. 
     
     
       17. The method of  claim 15 , wherein the first color is magenta, the second color is cyan or yellow, the third color is yellow or cyan, and the second and third colors are not the same. 
     
     
       18. The method of  claim 15 , wherein the first color is yellow, the second color is magenta or cyan, the third color is cyan or magenta, and the second and third colors are not the same. 
     
     
       19. The method of  claim 15 , wherein the rear reflector is white in color.